The present invention relates to a field emission device, an electron gun, a cathode ray tube apparatus, and a method of producing a cathode ray tube.
In recent years, flat display panels have started to be rapidly spread in the market. However, in the field of televisions of about 32 inches intended for home use, displays with cathode ray tubes (hereinafter xe2x80x9cCRTxe2x80x9d) still have an edge, with all things considered such as price and performance.
CRTs are provided with an electron gun as an electron emission source.
Conventional electron guns include a thermal cathode made up of a nickel cylinder in which a heater is placed, whose outer surface is covered with oxide that is mainly composed of barium oxide (BaO).
In the electron gun, an oxide layer will emit electron beams by being applied heat from the heater of the thermal cathode.
Displays are required to have a high-resolution performance, in order to deal with environmental changes such as full-scale introduction of terrestrial digital broadcasting. In order to realize a high-resolution performance in CRTs, it is necessary to improve current density at the thermal cathode. In fact, an extent of improvement required for the current density is great as much as by 6 to 10 times the normal thermal cathode currently used for CRTs.
There have already been attempts for improving current density at the thermal cathode, such as by technically improving materials, which, however, are reaching the physical limit. That is, with CRT, it has come to a point where it is difficult to dramatically improve the current resolution.
On the other hand, research and development has started recently attempting to replace the thermal cathode with a cathode equipped with a field emission device.
A cathode equipped with a field emission device is characterized by inherently having high current density compared to a thermal cathode, therefore has been used for some products such as electron microscopes.
The field emission device has a structure in which a cathode electrode and an extraction electrode, both being a thin film, are formed in the stated order on a substrate, and having at least one emitter being a protrusion in a shape of cone on the cathode electrode. The extraction electrode has an opening above the emitter, and is electrically insulated from the cathode electrode by an insulating layer formed between the extraction electrode and the cathode electrode.
The cathode including this field emission device emits electron beams towards the anode (towards the screen in a CRT), by being applied voltage that exceeds a threshold value between the extraction electrode and the cone-shape emitter. The luminance is adjusted by altering the voltage to be applied.
The aforementioned cathode can operate with high current density, which was not possible with the thermal cathode. Furthermore, the CRT equipped with such a cathode in its electron gun has excellent characteristics in luminance and resolution.
Here, it is noted that the conventional CRTs have a problem in that, even with use of a field emission device as their cathode, the profile of electron beam on the screen (spot profile) will be distorted towards the edge of the screen. Such distortion in electron beams is more pronounced with higher luminance.
This problem with CRTs regarding the distortion of the spot profile of the electron beam is detailed with FIG. 14 as follows. FIG. 14 is a plan view showing a spot profile of the electron beam on each area of the CRT screen.
The spot profile of the electron beam, being largely affected by the horizontal deflection magnetic field generated by the deflection yoke, is changed according to an area of the screen which is irradiated with the electron beam as shown in FIG. 14.
As depicted in FIG. 14, in the center of the screen, the spot profile P1 is yielded in a perfect circle form; and on the edges of the screen (either left or right of the screen in FIG. 14), the spot profile P2 is yielded in a laterally-long oval form.
Furthermore, in corner parts of the edges of the screen (either upper or lower parts), the spot profile P3 is yielded in an oval form being long in a slanting direction.
The aforementioned distortion in spot profiles of the electron beam is generated since the collision angle of the electron beam on the screen is different according to each position of the screen. This is because the electron beam emitted from the electron gun comes into collision with the screen, after being deflected by the deflection magnetic field that is a combination of a horizontal deflection magnetic field and a vertical deflection magnetic field.
The electron beam having distortion in a horizontal direction, in particular, will greatly deteriorate an effective resolution of a CRT.
As shown in FIG. 14, the spot profile of the electron beam is largely affected by the horizontal deflection magnetic field of a deflection yoke.
In order to solve this problem, an electron gun whose electron lens is equipped with a quadrupole lens has been proposed. However, such electron gun is problematic because of the cost increase due to the increase in parts.
Under such circumstances, Japanese Laid-open Patent Application H07-147129 disclosed a technology for improving the distortion in spot profiles without using a quadrupole lens.
The structure of the cathode disclosed by this prior art is shown in FIG. 15.
In FIG. 15, three electron emission areas 515a, 515b, and 515c are formed on a surface of a substrate 511. The form of each electron emission area is as follows: the electron emission area 515a that positions in the center has a perfect circle form; and the electron emission areas 515b and 515c, each positioning at top and bottom, have a crescent form. A cathode electrode 512a is connected to the electron emission area 515a positioning in the center, and a cathode electrode 512b is connected to the other electron emission areas 515b and 515c. The cathode electrode 512b is electrically separate from the cathode electrode 512a. 
This cathode emits electron beams directed to the center of the screen, only from the electron emission area 515a, and emits electron beams directed to the edge areas of the screen, from all the electron emission areas 515a, 515b, and 515c. That is, this cathode is able to emit the electron beam having a perfect circle form, for the center of the screen, and to emit the electron beam having an oval form which is long in a vertical direction, for the edge areas of the screen.
Although the disclosed technology is able to improve the distortion of the electron beam to some extent, it cannot perform an appropriate correction to the distortions created throughout the screen, because the forms of the electron emission areas are limited to two patterns, either a perfect circle form or an oval form which is long in a vertical direction. More specifically, the aforementioned technology is not able to either perform a correction for horizontally distorted spot profiles, or an appropriate correction according to each position at the screen.
Furthermore, the cathode, having a field emission device, has a problem that the electron emitting performance will decrease as an elapse of driving time of the device.
When the degree of vacuum in the CRT is low, the electron emitted from the field emission device comes into collision with the gas remaining within the tube, thereby generating ions, and the generated ions come into collision with the surface of the field emission device, resulting in the device being damaged. The device damaged in the above way will have degraded electron emission performance, and will cause luminance deterioration.
As seen in the above, one reason causing the deterioration in the device is the generation of ions due to the low degree of vacuum within the CRT. Generally, the degree of vacuum in a CRT is about 10xe2x88x925(Pa). Currently, a great improvement cannot be expected in the vacuum degree due to a limitation in the production process and the like.
Another reason causing the deterioration in the device is a current density at the time of operating the cathode. Within a CRT, a field emission device in its operating state may be driven at a current density of about 10(A/cm2). This value is one digit larger than the value of the thermal cathode.
If only for achieving an object of preventing the device deterioration, the current density of the device may be kept low. However, in view of the object for maintaining high luminance as mentioned earlier, the current density for the device should not be low.
The object of the present invention, in view of the stated problems, is to provide a field emission device that emits an electron beam bundle whose form on the display surface has little distortion, and that is able to maintain a stable electron emission property regardless of a length of time for which the device has been driven. The present invention also intends to provide a cathode ray tube apparatus equipped with such field emission device, and a method of producing a cathode ray tube equipped with such field emission device.
In order to achieve the stated object, the present invention is characterized by a field emission device that emits electron beams in a bundle to be scanned over a screen, including: a plurality of electron emission zones arranged two-dimensionally, each of which is driven independently of the other electron emission zones and emits an electron beam by means of an electric field.
In the Japanese laid-open patent application H07-147 129, an electron emission area is divided into three or more in advance. The cathode having such electron emission area corrects distortion of a spot profile of the electron beam, by driving each divided area independently of the other areas. However, such cathode is only able to correct the distortion in one direction that has been set in advance.
On the other hand, in the field emission device of the present invention, a plurality of electron emission zones are provided two-dimensionally, each of which is driven independently. Therefore, by arbitrarily selecting electron emission zones located in a matrix configuration and driving the selected electron emission zones, the spot profile of the resulting electron beam bundle can be corrected in a horizontal direction as well as in a vertical direction (i.e. scanning direction of an electron beam). Accordingly, the field emission device of the present invention is superior to the cathode in the aforementioned prior art, in that it can emit electron beam bundles whose spot profile is not distorted much, on any part of the screen.
Here, each of the plurality of electron emission zones according to the present invention is able to emit an electron beam independently of each other, and selection of appropriate electron emission zones from which electron beams are emitted in a bundle is possible with the present invention so as to yield a spot profile on the screen having little distortion, according to an area of the screen to be irradiated with the electron beam bundle. In addition, the configuration in which the electron emission zones are disposed is two-dimensional, unlike the one-dimensional configuration depicted in the aforementioned FIG. 15. The electron emission zones disposed in this way each correspond to the three electron emission zones depicted in FIG. 15.
Here, it should be noted that many electron emission zones are provided with a plurality of electron-beam emitters disposed two-dimensionally. However, an emitter cannot emit an electron beam independently of each other, therefore does not correspond to the electron emission zone of the present invention.
Here, it is desirable that the electron emission zones are each made up of at least one emitter.
It is also desirable that the electron emission zones are arranged in a matrix configuration.
Concretely, the field emission device of the present invention desirably has, in addition to the emitters, a substrate, a plurality of row electrodes provided parallel to each other on the substrate, and a plurality of column electrodes parallel to each other and provided over the plurality of row electrodes with an insulating layer in-between, the column electrodes crossing over the row electrodes, where the at least one emitter is disposed at each of crossover portions formed between the row electrodes and the column electrodes, so as to protrude from a row electrode. The stated construction is desirable in view of driving each one of the electron emission zones independently, without a complicated control circuit.
Specifically, the emission of such electron beam bundle from such electron emission zones is made possible by controlling voltage applied between row electrodes and column electrodes.
In addition, the electron gun of the present invention emits an electron beam in a bundle to be scanned over a screen, and has: a field emission device including a plurality of electron emission zones arranged two-dimensionally, each of which being driven independently of the other electron emission zones, and emits an electron beam by means of an electric field; and an electron lens accelerating and converging the electron beam bundle.
In the field emission device of this electron gun, a plurality of electron emission zones are provided two-dimensionally, each of which is driven independently. Therefore, the sectional form of the electron beam bundle at the time of emission is changed in all directions of the screen including a horizontal direction (i.e. a scanning direction of the electron beam bundle).
Here, the aforementioned electron emission zones disposed two-dimensionally are able to emit an electron beam independently of each other, and correspond to the three electron emission zones depicted in FIG. 15.
Here, it is desirable that the aforementioned electron gun has a detection unit that detects distortion of a spot profile of the electron beam bundle emitted from the emitters, and that its electron lens includes a rotation unit operable to rotate the electron beam bundle around an axis that coincides with the direction of the electron beam bundle, so as to correct the distortion based on the detection result of the detection unit.
Such electron gun whose electron lens includes a rotation unit is able to emit an electron beam bundle whose spot profile on the screen will be less distorted even on the corner of the screen, than an electron gun without such a rotation unit.
Furthermore, in the electron gun of the present invention, at least one of the field emission device and the electron lens is preferably equipped with a deferential exhausting unit made of a getter material, with a view to maintaining a good electron emission performance. Therefore, in the electron gun having the stated construction, even if it is equipped with a field emission device with a high current density, its electron emission performance will not decrease throughout the operation.
In addition, a cathode ray tube apparatus of the present invention is characterized by including: a field emission device where a plurality of electron emission zones are arranged two-dimensionally, each electron emission zone emitting, by means of an electric field, an electron beam independently of the other electron emission zones; an electron lens accelerating and converging electron beams emitted in a bundle; and a deflection yoke deflecting the electron beam bundle before the electron beam bundle is scanned over a screen which is placed to oppose the deflection yoke.
In the stated cathode ray tube apparatus, the field emission device has a plurality of electron emission zones that are provided two-dimensionally, each of which is driven independently of the other electron emission zones. Therefore, the sectional form of the electron beam bundle at the time of emission is changed in all directions of the screen including a horizontal direction (i.e. a scanning direction of the electron beam bundle).
Furthermore, in the aforementioned cathode ray tube apparatus, it becomes possible to correct the sectional form of an electron beam bundle at the time of emission, according to the distortion generated at the electron beam bundle by the deflection yoke. This enables to optimally correct the distortion of the spot profile of the electron beam bundle on the screen, throughout the surface of the screen.
Therefore, the cathode ray tube apparatus of the present invention is capable of emitting an electron beam bundle having little distortion in form on the screen, regardless of an area of the screen irradiated with the electron beam bundle.
Here, the plurality of electron emission zones, just as mentioned above, are able to emit an electron beam independently of each other, and correspond to the three electron emission zones depicted in FIG. 15.
Furthermore, in the present invention, a method of producing a cathode ray tube includes: a storing step of storing an electron gun in a neck part of a funnel, the field emission device being included in the electron gun and emitting an electron beam bundle by means of an electric field; a connecting step of connecting the funnel to a panel; and an aging step of degassing a space formed between the funnel and the panel, where the field emission device has a plurality of electron emission zones arranged two-dimensionally, each of which emitting, by means of an electric field, an electron beam independently of the other electron emission zones, and the aging step is performed by generating ion by making electron emission zones positioning in an edge of the field emission device emit electron beams, and making the electron emission zones from which the electron beams are emitted absorb the generated ion.
In the aforementioned method of producing the cathode ray tube, during the degassing aging process, the degree of vacuum is improved within the cathode ray tube, in particular in the vicinity of the field emission device.
In addition, according to the production method of the present invention, the generated ion is absorbed by the electron emission zones positioning at the edges of the device, thereby preventing the reduction of luminance at the time of driving the cathode ray tube produced using the method.
Therefore, in the cathode ray tube produced using this method, the electron emission performance of a field emission device will not decrease much during the operation.